Obesity is a risk factor for several adult chronic diseases. Obesity is more prevalent among African-Americans (AA) than other ethnic groups, especially AA females. Obesity tracks from childhood into the adult years. Children above the 50th percentile (50 percent tile) and/or who have one or two obese parents are more likely to become obese than others. Thus, intervening just before and early in puberty among those at high risk may prevent obesity among those not already obese, and prevent or minimize further weight gain among those already overweight and lower chronic disease burden. We hypothesize that participation in 60 min or more per day of moderate to vigorous physical activity, eating 5 or more servings of fruit, juice and vegetables (FJ and V) per day, and decreasing dietary fat intake will minimize weight gain over a two year period among prepubertal 8-year-old (yo) AA girls in the upper 50 percent tile of BMI or who have one or more obese parents. Behavioral objectives will be achieved through a 2-year intervention consisting of a four-week summer day camp and a 23 month child-parent weekly interactive Fun, Food and Fitness web site to learn about healthy eating and physical activity. This study will employ a randomized two group (treatment-control) design with four annual repeated measures at baseline, mid program (+12 mo), post program (+24 mo), and a year after the program(+36 mo) starting with 336 girls. The primary intervention outcomes will be body weight and fat gain as measured by DEXA; secondary outcomes include cardiovascular disease risk factors, energy expenditure measured by doubly labeled water, dietary practices and psychosocial variables. Candidate gene polymorphisms and resting metabolic rate will be examined for association with obesity related phenotypes and response to intervention. Prior to the Intervention (Phase I) we will initiate three studies: 1) test of the validity of two alternative approaches to self-report of physical activity (24-hour physical activity recall vs. week activity recall); 2) assessment of family and personal factors that influence physical activity among these girls; and 3) development and pilot testing of a culturally sensitive month-long summer camp and two month world wide web program to help 8yo AA girls change their dietary and physical activity practices. This will be the first obesity prevention project to employ a month-long summer camp, web technology, and sophisticated biological measures to assess factors predictive of body composition change.